Transcript Worms - Mrs. aRusso`s 7th/8th Grade Science Site!

Worms
Mrs. aRusso
Grade 7- Life Science
General Characteristics of Worms
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Slender, legless invertebrates
Have organs (digestive, reproductive, etc.)
Show bilateral symmetry (matching halves)
Have an anterior (head) and posterior (tail)
Some reproduce sexually (2 parents) and
some reproduce asexually (1 parent)
– Regeneration- type of asexual reproduction where
organism re-grows missing parts.
• Are either free-living or parasitic
• Free living: lives on its own; independent
• Parasitic: lives in or on another organism
harming it in some way.
• Host: the organism that a parasite lives in or
on
Earthworms
• Earthworms are free-living
• Earthworms belong to the Annelid phylum
which contains the segmented worms.
Earthworm Anatomy
• Anatomy = the study of structure or internal
workings of an organism.
Digestive System
• Responsible for breaking down food and
absorbing nutrients; earthworms are “tubes
within tubes” with two openings: mouth and
anus
Digestive System Parts/Information
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A.) Mouth- food enters here
B.) Pharynx- pulls in food
C.) Esophagus- food is moistened here
D.) Crop- Storage area for food before it gets
digested
• E.) Gizzard- contains small stones/sand that
shred/grind up food (physical digestion)
Digestive System Parts/Information
• F.) Intestines:
– Makes up 2/3 of the digestive system’s length
– Food is completely broken down and absorbed for
use by the rest of the body (chemical digestion)
• G.) Anus: solid waste (called castings) exits
here
• Peristalsis: rhythmic contractions that push
food through the digestive system.
Excretory System
• Responsible for getting rid of waste
• Liquid waste exits through the skin
Circulatory System
• Blood is pushed through two major blood
vessels by the pumping of 5 sets of “hearts”
(AKA aortic arches).
• Blood carries nutrients absorbed from the
intestines and oxygen to all parts of the body.
• Blood also carries carbon dioxide.
Respiratory System
• Controls the intake of air
• Air enters an earthworm through its skin
Reproductive System
• Each earthworm has BOTH male and female
reproductive organs.
Sexual Reproduction in the Earthworm
• Worms have both eggs and sperm.
• 2 worms exchange sperm and both end up with
fertilized eggs.
• ----------------------------------------------------------------• Clitellum: a thick band found near the
earthworm’s head. The creates a foam ring
which will contain the egg and sperm.
• Cocoon: this is the foam ring. Eggs and sperm
unite here (fertilization). The cocoon is left
behind by the worm. The young worms usually
hatch from the cocoon.
Movement
• Earthworms can bend at each segment. They
can move because they have two sets of
muscles and setae. When one set contracts
(shortens), the other set relaxes.
– Setae- bristles located on each segment that are
used to grip soil.
Niche
• An organism’s role in the environment (AKA
“job”)
Earthworm’s Niche
• Enrich the soil through its castings
• Make tunnels in the soil for water and air
(helps plants)
Other Examples of Segmented Worms
• Leeches: parasitic
• California Black worm: Freshwater, free-living
worms that can asexually reproduce through
regeneration. Belong to the Annelid phylum.